Duplex radio system



W. E. REICHLE 4 DUPLEX RADIO SYSTEM Nov. 26, 1940.

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AT TORNEV Patented Nov. 26, 1940 UNITED STATES PATENT OFFICE DUPLEXRADIO SYSTEM Application May 25, 1939, Serial No. 275,610

11 Claims.

The invention relates to power supply arrangements for vacuum tubeapparatus, radio communication systems and the like and moreparticularly to arrangements in which alternating current is convertedinto pulsating current which is then filtered and supplied to a loadcircuit.

A specific application of the invention is to a duplex radio system inwhich a single power supply is connected alternately to a radiotransmitter and a radio receiver. To permit of this common use of thepower supply and for other practical reasons the radio transmitter andradio receiver are conveniently designed to operate with nearly the samemaximum voltage from the power supply. Commonly, however, thetransmitter draws a considerably larger load current than the receiver,in order that the power output of the transmitter may be sufiicient forcommunica tion to the desired distance. The power supply is required topossess sufliciently good regulation to permit it to supply either ofthese diverse loads in a satisfactory manner or else some compensationmust be made each time the load is changed. In power supply devices nowin use 25 the filter serves as a voltage regulating device to a greateror less degree in addition to its function of smoothing out thepulsations or power ripples. The filter is usually of the low pass typecomprising one or more series inductances and 30 one or more shuntcapacitances, the degree of regulation being greater if the filterterminates in a series inductance at the input side than it is if ashunt capacity termination is employed. The shunt termination, however,is known to pro- 5 vide higher terminal voltages at all current loadsand accordingly to give a somewhat larger power output than can beobtained with the series termination. In commercial apparatus where itis desired to operate the vacuum tubes at maximum 40 power output theadvantage of the shunt termination will be evident, but the terminalvoltage developed by the shunt terminated filter when supplying therelatively small current drawn by the radio receiver is in most casesvery likely to 6 be excessive.

In accordance with the invention auxiliary contacts are provided on theswitch or relay used to transfer the power supply from the transmitterto the receiver and vice versa. The auxiliary 50 contacts serve to alterthe termination of the filter simultaneously with the change from oneload condition to the other. In a specific embodiment of the inventionthe filter is normally terminated in a series inductance or choke coiland is so employed when connected with the radio receiver.

When the output of the filter is switched over to connect with the radiotransmitter a shunt condenser is simultaneously switched into operationahead of the series inductance, thereby converting the filter into onehaving a shunt capacity 5 termination. With this arrangement, thevoltage impressed upon the radio receiver by the power supply is held toa safe value and when the radio transmitter is in operation the poweroutput radiated is considerably greater than would 1 be the case if thefilter termination were left unchanged when the power supply is shiftedfrom the receiver to the transmitter.

To reduce or eliminate sparking at the contacts through which the shuntcondenser is con- 15 nected across the power supply circuit, thecondenser may be permanently connected in place with a high resistancein series therewith. The resistance may be sufiiciently large to preventthe condenser from raising the terminal voltage apgo preciably while thefilter is connected to the radio receiver and the relay contacts may beemployed to short-circuit the resistance when the filter is connected tothe radio transmitter.

The single figure of the accompanying drawing shows an embodiment of theinvention in a duplex radio communication system.

In the drawing, I is a radio transmitter and 2 is a radio receiver,either of which may be connected to a common antenna 3 by means ofcontacts operated by a relay winding 4 of an ordinary antenna transferrelay. Terminals 5 and 3 are for connection to an alternating currentsource such as commercial 60-cycle supply mains. The terminals 5 and 6are connected to the primary winding of a conventional power supplytransformer I having secondary windings for impressing voltages upon afull wave rectifier 8 and for supplying heating current to the filamentsof the rectifier. A power supply filter 9 which embodies certainfeatures of the invention is connected to the output of the rectifier. Arelay winding I0 controls various contacts including main contacts fortransferring the output connection of the filter 9 from the radioreceiver to the radio transmitter and vice versa and also an auxiliarycontact for carrying out purposes of the invention. The rectangle llencloses additional filtering elements and potential dividingarrangements of a conventional nature which are used in connection withthe radio receiver. A manually operated key l-2 controls the relays 4and Ill, through an intermediary relay l3, to place and maintain thesystem in the transmitting condition as will be more fully describedhereinafter.

The filter 9 normally terminates at its input side in a seriesinductance or choke coil I4. The filter illustrated is of very simpledesign, including in addition to the coil I4 a shunt condenser I5.Another shunt condenser I6 is for use only in the transmittingcondition. In series with the condenser I6 across the input side of thefilter 9 is a high resistance I1 and a switch I8.

Associated with the relay winding I is a main armature I9 cooperatingwith a front contact 20 and a back contact 2|, armature I9 and contact2| normally completing a circuit from the positive terminal of theoutput side of filter 9 to one of the input terminals of device II. Therelay winding III has another main armature 22 and associated contact 23which are connected together only in the transmitting condition. Contact20 is permanently connected to the plate and screen grid supply circuitsof the radio transmitter through a lead 24. Contact 23 is connected tothe negative end of a self-biasing resistor 25 in the radio transmitterby means of a lead 26.

There is also associated with the relay winding III an. auxiliaryarmature 21 and a contact 28 which are also connected together only inthe transmitting condition. The armature 21 is connected through a lead29 to one end of the resistance II. The contact 28 is connected througha lead 30 and the switch I8 to the opposite end of the resistance II.

In the normal or receiving condition the positive terminal of the filter9 is connected through armature I9, contact 2| and the inner connectionsof device II to ground and thence through a lead 3| in the radiotransmitter to the positive terminal of resistance 25 and to one side ofkey I2. The other side of key I2 is connected through a lead 32 to arelay winding I3 and thence by a lead 33 to the negative side of filter9. The relay winding I3 is associated with an armature 34 and a contact35, the armature being connected to one side of the alternating currentsupply by means of a lead 36 and the other side of the alternatingcurrent supply being connected through a lead 31 to the relay windings 4and III in parallel and thence through a lead 38 to contact 35.

The radio transmitter I and radio receiver 2, being conventional and.forming no part of this invention, are only partially illustrated, suchdetails being shown as are considered necessary to a full explanation ofthe invention.

In the operation of the system, let it be assumed that the terminals and6 are connected to a suitable source of alternating current and that theradio system is in the receiving or stand-by condition. The relaywindings 4, I0 and. I 3 are all deenergized and their contacts are inthe position shown in the figure. The alternating current passes throughthe transformer I and is converted into a pulsating unidirectionalcurrent by therectifier 8 in well-known manner, the pulsating currentbeing impressed upon the input side of the filter 9. The filtered outputcurrent passes through armature I9 and contact 2| to the auxiliaryfilter and potential divider II, returning to the negative side of thefilter. Various potentials from the potential divider are applied to theanodes, screen grids and control grids in the radio receiver in theusual manner, some of the connections being indicated in the figure. Theantenna '3 is connected to the input of the radio receiver through theback contact of the antenna transfer relay 4, the radio transmitter isdisconnected from the antenna at the front contact of relay 4 and thepower supply to the transmitter is out 01f at contacts 20 and 23. Inthis condition the filter 9 is eiiectively terminated on the input sidein the coil I4, the condenser I5 being ineffective and prevented fromcollecting any considerable electrical charge due to the seriesconnection of the resistance II. Alternatively, the switch I8 may beopen or the resistance Il may be omitted entirely, in either case theconnection of the condenser I6 to the negative side of the filter 3 isbroken at the contact 28.

To convert the system into the transmitting condition it is onlynecessary to depress the key I2 and thereafter the system will remain inthe transmitting condition until the key is released. By means of thekey, telegraph signals may be sent out in well-known manner or thesystem may be held in the active condition while the transmitter isbeing modulated with telephone signals, also in well-known manner. Forthe latter use, the key I2 is ordinarily mounted on the telephonetransmitter or microphone in a position to be operated conveniently bythe talker. A key thus used when talking is commonly called a "press totalk button.

When the key I2 is closed it completes a circuit from the positiveterminal of filter 9 through armature I9, contact 2| and device II toground, thence through lead 3| through the key contacts to relay windingI3 and to the negative side of filter 9. A current from the filterpasses through this circuit, energizing relay winding I3 and closing thecircuit between armature 34 and contact 35 associated with relay windingI3. This relay, is preferably a relatively sensitive one so as to becapable of operation on a small current obtainable from the power supplyin the receiving condition. Relay I3 closes an obvious alternatingcurrent path from terminals 5 and 6 through the relay windings 4 and I0in parallel to effect the final switching operations. The relay 4transfers thev antenna from the radio receiver to the radio transmitterin well-known manner. The relay I0 transfers the connection from thepositive terminal of the filter 9 from the auxiliary filter II to thelead 24 and the vacuum tube supply circuits of the radio transmitter, bytransferring the armature I9 from contact 2| to contact 20. The relayalso connects the negative side of the filter through the lead 26- tothe negative side of the grid biasing resistor 25 in the radiotransmitter. The latter connection, made by armature 22 and contact 23,completes the power supply circuit of the radio transmitter and at thesame time provides a new direct current supply circuit for the windingof, relay I3 to take the place of the circuit previously described whichis now broken at contact 2|. This substitute circuit is readily tracedfrom the positive terminal of the filter 9 through armature I9, contact20, the plate and screen grid circuits of the radio transmitters to thecathodes of the vacuum tubes which are connected to ground, and thence,as before, through the key I2 and winding I3 to the negative side of thefilter.

Simultaneously with the above-described switching of the power supplyfrom the receiving to the transmittingcondition, the relay I0 closes thecontact between its armature 21 and contact 28. This completes theconnection of the condenser IG as a shunt termination across the inputside of the filter 9. In case the switch I8 is open or the resistance IThas been omitted, the

armature 2! simply connects the free end of-the condenser IE to thenegative side of the filter. If the resistance I1 is provided and theswitch [8 is closed, the armature short-circuits the resistance H withthe same effect. The power is now supplied to the radio transmitter at ahigher terminal voltage than would have been obtained had the condenserl6 not been connected.

To restore the system to the receiving or standby condition it is merelynecessary to release key 12. This results in breaking the circuit ofrelay winding [3 causing that relay to release and in turn causingwindings 4 and III to become deenergized. Thereupon the antenna transferrelay returns the antenna to contact with the input of the radioreceiver and all the contacts of the relay l0 return to normal. Ifswitch I8 is open or resistance I! has been omitted, the separation ofarmature 21 and contact 28 may be attended by sparking due to aconsiderable charge on condenser !6. If, however, switch I8 is closedthe condenser is discharged through the resistance I'l, any suchtendency to sparking at the relay contacts is reduced or entirelyeliminated.

Numerous variations of the system illustrated, within the scope of theappended claims, will readily occur to those skilled in the art to whichthe invention appertains. For example, any two load circuits withunequal current requirements may be connected to the relay l0 instead ofthe radio transmitter and radio receiver. The relay l0 may be operateddirectly by arranging to have its circuit closed through the key l2instead of through the action of an intermediary relay l3, or, ifdesired, the switching may be accomplished manually. It is also evidentthat the relay or relays may be operated from any convenient source ofcurrent and may, if desired, be independent of the main power supply.The filter 9 may, of course, consist of any configuration of elementssuitable for the purpose and may contain additional sections as desired,provided only that one or more of the filter elements comprising part ofthe filter termination at the input side is arranged to have itsconnections changed simultaneously with the switching of the powersupply from one load to the other.

What is claimed is:

1. In a power supply system, a source of pulsating current, a filter forsmoothing out the pulsations of said current, a pair of load circuitswith diverse load requirements, means for connecting the output side ofthe filter at will to either load, and means coupled to said connectingmeans for altering the circuit configuration of the input termination ofthe filter to provide one terminating configuration when the first loadis connected and another terminating configuration when the second loadis connected.

2. In a power supply system, a source of pulsating current, a filter forsmoothing out the pulsations of said current, said filter being normallyterminated at its input side in a series inductance, a pair of loadcircuits with diverse load requirements, transfer means for connectingthe output side of the filter to either load circuit at will, acondenser, and means operating simultaneously with said transfer meansfor rendering said condenser effective as a shunt across the filterinput terminals when the filter output terminals are connected to oneload circuit and for substantially suppressing the shunting effect ofthe condenser when the filter output terminals are con nected to theother load circuit.

3. In a power supply system, a source of pulsating -current,a filter forsmoothing out the pulsations of said current, said filter beingterminated in a series inductance at its input side, a pair of load.circuits with diverse load requirements, transfer means for connectingthe output side of the filter to either load circuit at will, acondenser, and means operating simultaneously with said transfer meansfor connecting the condenser in shunt across the filter input terminalswhen the filter output terminals are connected to one load circuit andfor disconnecting the condenser when the filter output terminals areconnected to the other load circuit.

4. In a power supply system, a source of pulsating unidirectionalcurrent, a filter for smoothing out the pulsations of said current, twoload circuits, one of which draws a relatively large current compared tothe other, transfer means for establishing connections from the outputside of the filter to either load at will, and means coupled to saidtransfer means for altering the circuit configuration of the input sideof the filter simultaneously with the load transfer, in such manner asto provide a shunt input termination for the filter when connected tothe load drawing the larger current and a series input termination whenthe filter is connected to the load drawing the smaller current.

5. In a power supply system, a source of pulsating current, a smoothingfilter, said filter normally terminating at its input side in a seriesinductance, two load circuits, one of which draws a relatively largecurrent compared to the other, transfer means for connecting the outputside of the filter to either load circuit at will, a condenser, andmeans coupled to said transfer means for effectively connecting thecondenser in shunt across the filter input terminals when the filteroutput terminals are connected to the load which draws the largercurrent and for rendering the condenser ineffective as a shunttermination to the filter input when the filter output terminals areconnected to the load which draws the smaller current.

6. In a power supply system, a source of pulsating current, a smoothingfilter, said filter normally terminating at its input side in a seriesinductance, two load circuits, one of which draws a relatively largecurrent compared to the other, transfer means for connecting the outputside of the filter to either load circuit at will, a condenser, andmeans coupled to said transfer means for connecting the condenser inshunt across the filter input terminals when the filter output terminalsare connected to the load which draws the larger current and fordisconnecting the condenser when the filter output terminals areconnected to the load which draws the smaller current.

7. In a power supply system, a source of alternating current, arectifier, a smoothing filter normally terminated at its input side in achoke coil, a condenser and a large resistance connected in series witheach other and together shunted across the filter input terminals, theresistance being sufiiciently large to substantially eliminate thecondenser as an effective shunt element of the filter, a pair of loadcircuits requiring relatively large and small currents respectively, anda relay having main contacts and auxiliary contacts, said main contactsbeing arranged to connect the filter output to either load circuit undercontrol of the relay, and the auxiliary contacts being arranged toshort-circuit the said resistance when the load requiring relativelylarge current is connected and to remove the short circuit when theother load is connected.

8. In a duplex radio system, a radio transmitter, a radio receiver, asource of pulsating current, a filter for smoothing out the pulsations,means for connecting the output side of the filter to the currentutilizing circuits of either the radio transmitter or the radio receiverat will, and means'coupled to said connecting means for altering thecircuit configuration of the filter termination at the input side of thefilter to provide different terminations according to whether the filteris connected to the radio transmitter'or to the radio receiver.

9. In a duplex radio system, a radio transmitter, a radio receiver, asource of pulsating current, a filter for smoothing out the pulsations,said filter being terminated in a series inductance at its input side,transfer means for connecting the output'side of the filter to the radiotransmitter or to the radio receiver at will, a condensenand meanscoupled to said transfer means for connecting the condenser in shuntacross the'filter input terminals when the filter output terminals areconnected to the radio transmitter and for disconnecting the condenserwhen the filter output terminals are connected to the radio receiver.

10. In a duplex radio system, a radio transmitter, a radio receiver, asource of alternating current, a rectifier for converting alternatingcurrent from said source into a pulsating unidirectional current, afilter for smoothing out the pulsations, said filter being terminated ina series inductance at its input side, transfer means for connectingtheoutput side of the filter to the radio transmitter or to the radioreceiver at will, a condenser, and means coupled to said transfer meansfor connecting the condenser in shunt across the filter input terminalswhen the filter output terminals are connected to the radio transmitterand for disconnecting the condenser when the filter output terminals areconnected to the radio receiver.

11. In a duplex radio system, a radiotransmitter, a radio receiver, asource of alternating current, a rectifier for converting alternatingcurrent from said source into pulsating direct current, a smoothingfilter with input terminals connected to said rectifier, said filternormally terminating at its input side in a series inductance, acondenser and a large resistance connected in series with each other andin shunt'to the filter input terminals, the value of the resistancebeing sufiiciently great to substantially prevent the condenser fromacting as a shunt termination for the filter, and a relay having a mainset of transfer contacts and a pair of auxiliary contacts, the maincontacts being arranged to transfer the output of the filter from theradio transmitter to the radio receiver and vice versa, and theauxiliary contacts being arranged to short-circuit the said largeresistance simultaneously with transfer of

